The present invention relates generally to methods and apparatus for nondestructive radiographic examination of materials, and more particularly to a novel method and apparatus for the nondestructive inspection of composite wire.
Nondestructive testing procedures for routine examination of composite wire structural integrity, as, for example, in a production setting, have not been developed. Testing of composite wires is particularly difficult because existing manufacturing processes produce composite wire which may vary substantially in cross-sectional geometry and size, surface properties, and matrix/fiber composition. Because the intended use of the wire may frequently be as starting material in the fabrication of diffusion bonded composite structures comprising fabric or layers of the composite wire, wide variations in wire geometry, surface finish and composition may be tolerable without substantially affecting the quality of the fabricated composite structure. Nevertheless, because as-manufactured composite wire may be as just characterized, the nondestructive examination of finished wire for the existence of voids which significantly affect wire strength is extremely difficult using conventional methods. For example, nondestructive testing techniques based on observation of wire resistance, surface emissivity, ultrasonics, infrared imaging, and other familiar methods are often difficult to intercept because of these tolerated characteristics. Further, these familiar techniques are severely limited in their utility for examining wire quickly, in large quantity, or automatically. Wire imaging using radiographic techniques is also difficult because large lengths of wire must be examined with a resolution in the plane of the wire exceeding 50 line pairs per millimeter, which is difficult using detection techniques other than X-ray filming. The use of X-ray film for examining large quantities of wire, however, is not practical and would require a sophisticated image scanning densitometer, and the processing of huge amounts of data using some flaw detection algorithm.
The present invention eliminates or substantially reduces in critical importance the above described problems and inadequacies in existing nondestructive wire testing technology by providing a novel system and technique for examination of composite wire for the detection of voids or other composition anomalies. In the practice of the invention, a test wire is irradiated with penetrating radiation as the test wire is immersed in or drawn through a fluid bath having an attenuation coefficient for the radiation matching that of the material comprising a normal or standard wire. A pair of detectors adjacent the bath monitor the transmission of the radiation along separate paths through the bath and test wire and through the bath only, and compare the two transmissions to provide a measure of any voids extant in the test wire. Alternatively, the transmission through the bath and test wire may be compared to that through the bath and a standard or normal composition wire. Voids in the test wire are detected as severe composition anomalies. The fluid bath automatically adjusts to changes in wire size and geometry. Therefore, the technique of the present invention is independent of variations in test wire size or geometry, as might characterize as-manufactured composite wire, and readily identifies voids in the wire by observing changes in the average composition of the test wire. Though the specific embodiment disclosed utilizes X-ray, it is understood that other penetrating radiation, such as gamma or neutron radiation, used in conjunction with a fluid bath exhibiting appropriate attenuation characteristics may also be used within the scope of these teachings. The relative signal levels obtainable in detecting composition variations using this technique allow observation of void fractions in the composite wire of as low as about one percent.
It is, therefore, an object of the present invention to provide an improved nondestructive testing system and method.
It is a further object of the invention to provide a novel method for the nondestructive examination of wire.
It is yet a further object of the invention to provide an efficient and accurate system for the nondestructive testing of composite wire using penetrating radiation.
These and other objects of the present invention will become apparent as the detailed description of specific representative embodiments thereof proceeds.